Today the Northern Territory's land borders are defined to the west by the 129ð east longitude (<abbr title="129th meridian east longitude">129ð east</abbr>) with Western Australia, to the south by the 26th parallel south latitude (<abbr title="26th parallel south latitude">26ð south</abbr>) with South Australia and to the east by 138ð east longitude (<abbr title="138th meridian east longitude">138ð east</abbr>) with Queensland; however, this is not where all borders are actually marked on the ground.
The Northern Territory boundaries are shared with the West Australian border, the South Australian border, and the Queensland border.
In 1788, Governor Phillip claimed the continent of Australia as far west as the 135th meridian east longitude (<abbr title="135th meridian east longitude">135ð east</abbr>) in accordance with his commission. (26 January 1788 â Map)
On 16 July 1825, the western boundary of New South Wales was relocated to the line of <abbr title="129th meridian east longitude">129ð east</abbr> to take in the new settlement at Melville Island. (16 July 1825 â Map). From 1825 to 1829 129ð east was the NSW border.
Following the settlement of the Swan River Colony in 1829 (2 May 1829 â Map), its eastern boundary was declared to be 129ð east, coinciding with the western boundary of New South Wales at the time.
The colony of Western Australia (<abbr title="Western Australia">WA</abbr>) was commissioned in March 1831.
From 1829 to 1832, the SRC/NSW border was at 129ð east.
The name of the Swan River Colony was changed to Western Australia in 1832 (6 February 1832 â Map).
From 1832 to 1846, 129ð east was the <abbr title="Western Australia">WA</abbr>/<abbr title="New South Wales">NSW</abbr> border.
South Australia became a colony in 1836 and until 1846 would be surrounded on land by New South Wales (<abbr title="New South Wales">NSW</abbr>), with South Australia extending west to the 132ð east longitude. (<abbr title="132nd meridian east longitude">132ð east</abbr>) and north to <abbr title="26th parallel south latitude">26ð south</abbr> (28 December 1836 â Map).
From 1836 to 1846 <abbr title="129th meridian east longitude">129ð east</abbr> was the <abbr title="Western Australia">WA</abbr>/<abbr title="New South Wales">NSW</abbr> border. <abbr title="132nd meridian east longitude">132ð east</abbr> was the <abbr title="South Australia">SA</abbr>/<abbr title="New South Wales">NSW</abbr> border as were <abbr title="26th parallel south latitude">26ð south</abbr> and <abbr title="141st meridian east longitude">141ð east</abbr>.
In 1846 the colony of North Australia (<abbr title="North Australia">NA</abbr>) was proclaimed by Letters Patent, which was all of New South Wales north of <abbr title="26th parallel south latitude">26ð south</abbr> (17 February 1846 â Map).
From 1846 to 1847 <abbr title="129th meridian east longitude">129ð east</abbr> was the <abbr title="Western Australia">WA</abbr>/<abbr title="New South Wales">NSW</abbr> border and the <abbr title="Western Australia">WA</abbr>/<abbr title="North Australian">NA</abbr> border. <abbr title="132nd meridian east longitude">132ð east</abbr> was the <abbr title="South Australia">SA</abbr>/<abbr title="New South Wales">NSW</abbr> border, while <abbr title="26th parallel south latitude">26ð south</abbr> became the <abbr title="South Australia">SA</abbr>/<abbr title="North Australia">NA</abbr> border and <abbr title="141st meridian east longitude">141ð east</abbr> remained the <abbr title="South Australia">SA</abbr>/<abbr title="New South Wales">NSW</abbr> border.
In 1847 the colony of North Australia was revoked and reincorporated into New South Wales. (15 April 1847 â Map), so South Australia was once again surrounded by New South Wales on all land borders.
From 1847 to 1860 <abbr title="129th meridian east longitude">129ð east</abbr> was once again the <abbr title="Western Australia">WA</abbr>/<abbr title="New South Wales">NSW</abbr> border.
From 1847 <abbr title="132nd meridian east longitude">132ð east</abbr> was again the <abbr title="South Australia">SA</abbr>/<abbr title="New South Wales">NSW</abbr> border, and <abbr title="26th parallel south latitude">26ð south</abbr> was also the <abbr title="South Australia">SA</abbr>/<abbr title="New South Wales">NSW</abbr> border. <abbr title="141st meridian east longitude">141ð east</abbr> would remain the <abbr title="South Australia">SA</abbr>/<abbr title="New South Wales">NSW</abbr> border until 1851.
In 1851 South Australia's eastern border changed again when the colony of Victoria was proclaimed (1 July 1851 â Map).
From 1851 <abbr title="141st meridian east longitude">141ð east</abbr> would change to include both the <abbr title="South Australia">SA</abbr>/<abbr title="New South Wales">NSW</abbr> border and the <abbr title="South Australia">SA</abbr>/<abbr title="Victorian">VIC</abbr> border.
In 1859 The colony of Queensland is proclaimed by Letters Patent, with its western border set at <abbr title="141st meridian east longitude">141ð east</abbr> (6 June 1859 â Map).
From 1859 <abbr title="141st meridian east longitude">141ð east</abbr> would change to include the <abbr title="South Australia">SA</abbr>/<abbr title="Queensland">QLD</abbr> border, the <abbr title="South Australia">SA</abbr>/<abbr title="New South Wales">NSW</abbr> border and the <abbr title="South Australia">SA</abbr>/<abbr title="Victorian">VIC</abbr> border.
In 1860 the western border of South Australia changed from <abbr title="132nd meridian east longitude">132ð east</abbr> to <abbr title="129th meridian east longitude">129ð east</abbr> (1860 â MAP).
From this time on South Australia's western border was also the West Australian border.
From 1860 <abbr title="129th meridian east longitude">129ð east</abbr> became the <abbr title="South Australia">SA</abbr>/<abbr title="Western Australia">WA</abbr> border from south of <abbr title="26th parallel south latitude">26ð south</abbr> & the <abbr title="Western Australia">WA</abbr>/<abbr title="New South Wales">NSW</abbr> border north of <abbr title="26th parallel south latitude">26ð south</abbr>.
In 1862 Queensland's western border north of <abbr title="26th parallel south latitude">26ð south</abbr>) was moved to <abbr title="139th meridian east longitude">139ð east</abbr> (1862).
From 1862 <abbr title="26th parallel south latitude">26ð south</abbr> became shared as the <abbr title="South Australia">SA</abbr>/<abbr title="New South Wales">NSW</abbr> border and the <abbr title="South Australia">SA</abbr>/<abbr title="Queensland">QLD</abbr> border between <abbr title="139th meridian east longitude">139ð east</abbr> and <abbr title="141st meridian east longitude">141ð east</abbr>.
In 1863 that part of New South Wales to the north of South Australia was annexed to South Australia by Letters Patent as "the Northern Territory of South Australia", which was shortened to "the Northern Territory" (6 July 1863 â Map).
From 1863 to 1911 <abbr title="129th meridian east longitude">129ð east</abbr> was the <abbr title="Western Australia">WA</abbr>/<abbr title="Northern Territory of South Australia">NToSA</abbr> border north of <abbr title="26th parallel south latitude">26ð south</abbr> & the <abbr title="Western Australia">WA</abbr>/<abbr title="South Australia">SA</abbr> border south of <abbr title="26th parallel south latitude">26ð south</abbr>. <abbr title="26th parallel south latitude">26ð south</abbr> became the <abbr title="South Australia">SA</abbr>/<abbr title="Northern Territory of South Australia">NToSA</abbr> border.
In 1911 the Northern Territory was split off from South Australia to be administered by the Commonwealth. (1 January 1911 â Map).
From 1911 to 1927 <abbr title="129th meridian east longitude">129ð east</abbr> was the <abbr title="Western Australia">WA</abbr>/<abbr title="Northern Territory">NT</abbr> border north of <abbr title="26th parallel south latitude">26ð south</abbr> & the <abbr title="Western Australia">WA</abbr>/<abbr title="South Australia">SA</abbr> border to the south. <abbr title="26th parallel south latitude">26ð south</abbr> became the <abbr title="South Australia">SA</abbr>/<abbr title="Northern Territory">NT</abbr> border.
In 1927 the Northern Territory was split into two territories, North Australia and Central Australia, with the border set at the <abbr title="20th parallel south latitude">20ð south</abbr>. (1 March 1927 â Map).
From 1927 <abbr title="26th parallel south latitude">26ð south</abbr> became the <abbr title="South Australia">SA</abbr>/<abbr title="Central Australia">CA</abbr> border.
In 1931 North Australia and Central Australia were reunited as the Northern Territory (12 June 1931 â Map).
From 1931 <abbr title="26th parallel south latitude">26ð south</abbr> once again became the <abbr title="South Australia">SA</abbr>/<abbr title="Northern Territory">NT</abbr> border.
Marking the Northern Territory borders on the ground has a fascinating history.
The West Australian border with the Northern Territory and South Australia, which has been marked on the ground, is not as straight as it looks, with the <abbr title="Western Australia">WA</abbr>/<abbr title="Northern Territory">NT</abbr> and <abbr title="Western Australia">WA</abbr>/<abbr title="South Australia">SA</abbr> borders being displaced by approximately 127 m, due to early survey errors within the limits of technology available in the 1920s.
The 127-metre section that runs eastâÂÂwest along the <abbr title="26th parallel south latitude">26ð south</abbr> is part of the border between Western Australia and the Northern Territory. In June 1968, two monuments were erected to mark each end of this 127-metre sideways section; the easternmost of these monuments, being where all three borders meet, was named Surveyor Generals Corner.
Also known as Poeppels Corner in Queensland, at latitude 26ð S and longitude 138ð E, this is a corner of state boundaries, where the state of Queensland meets South Australia and the Northern Territory.